1. Field of Invention
The invention relates to an optical drive control method, and, in particular, to a method for setting a layer-jump point of a multilayer optical disc.
2. Related Art
In general, when data is accessed on a double-layer optical disc by an optical drive, an optical pickup head of the optical drive has to be moved to a proper position to perform focusing and track seeking operations. As shown in FIG. 1, a double-layer optical disc 1 is disposed in an optical drive 2 (indicated by a dashed line) and held at a naturally balanced position D0. The double-layer optical disc 1 has two reflective layers 11 and 12 for storing data. A laser spot of an optical pickup head 21 of the optical drive 2 is focused on the reflective layer 11 of the double-layer optical disc 1. A servo controller 24 controls an actuator 22 to move the optical pickup head 21 to change a focus position F0 of the laser spot of the optical pickup head 21 (shown in FIG. 2A). In addition, the servo controller 24 also controls a spindle motor 23 to rotate the double-layer optical disc 1. The actuator 22 generates a control force Fc to move the optical pickup head 21 to the proper position such that the optical pickup head 21 can move the focus position F0 from the naturally balanced position D0 to a focus position on the reflective layer 11 or the reflective layer 12.
As shown in FIGS. 2A and 2B, the control force Fc generated by the actuator 22 is properly controlled such that the optical pickup head 21 is moved from a position D1 to a position D2, and the focus position F0 of the optical pickup head 21 can be correctly moved from the reflective layer 11 (see FIG. 2A) to the reflective layer 12 (see FIG. 2B). In contrast, the control force Fc generated by the actuator 22 may also move the optical pickup head 21 from the position D2 to the position D1, such that the focus position F0 of the optical pickup head 21 is moved from the reflective layer 12 (see FIG. 2B) to the reflective layer 11 (see FIG. 2A). Consequently, the data may be accessed on the reflective layer 11 or the reflective layer 12 by the optical pickup head 21.
However, because the double-layer optical disc 1 does not have uniform weight distribution over its area, the rotating disc may shake up and down. As shown in FIG. 3, when the double-layer optical disc 1 is rotating, the double-layer optical disc 1 shakes up and down relative to the naturally balanced position D0 such that the control force Fc generated by the actuator 22 cannot move the focus position F0 of the optical pickup head 21 from the reflective layer 11 to the reflective layer 12, or from the reflective layer 12 to the reflective layer 11. Thus, the data cannot be accessed on different layers of the double-layer optical disc 1 by the optical drive 2.
Consequently, it is an important subject of the invention to provide a method for setting a proper layer-jump point of the optical disc in response to the up-and-down shaking of the optical disc in order to access the data on different layers of the disc successfully.